Technical Field
The present disclosure relates to a shielded cable, and more particularly, to a shielded cable including signal wires of which two signal conductors are covered with insulators respectively, and a shield conductor having a metal clad resin tape spirally wrapped around the signal wires in a lump.
Related Art
A shielded cable having a plurality of, for example two signal wires as a pair is used to transmit a digital signal in a differential transmission method. According to the differential transmission method, signals a phase of which has been reversed by 180° are input into a pair of signal wires at the same time and are transmitted, and the difference of the signals is detected at a receiver. Thereby, it is possible to double a signal output. Also, a noise signal is equally applied to the pair of signal wires through a transmission path ranging from a sender to a receiver. For this reason, the noise signal is cancelled upon the output at the receiver, so that the noise can be removed.
The pair of signal wires is shielded by a metal foil. However, since the metal foil does not have enough mechanical strength, a metal clad resin tape where a metal foil is attached to a resin tape is used. When the metal clad resin tape are wrapped spirally around the signal wires while a part thereof is overlapped, the overlapped part of the tape is not electrically connected, so that a suck-out phenomenon (dip of signal) may be generated in a high frequency region. Therefore, Patent Document 1 discloses a technology that the metal foils of an upper turn and a lower turn are in contact at the overlapped part.
[Patent Document 1] Japanese Patent Application Publication No. 2011-222262A
In the shielded cable, characteristic impedance is set so that a favorable signal transmission characteristic is obtained in a usable frequency region. The characteristic impedance is varied as a section of the signal wire is deformed. Patent Document 1 does not disclose a relation between the change in the characteristic impedance and the deformation of the signal wire.